生物制氢反应器产氢产乙酸菌群对挥发酸的转化

采用间歇培养的方式,利用取自生物制氢反应器的厌氧活性污泥考察了活性污泥中产氢产乙酸菌群对乙醇、乙酸、丙酸、丁酸、戊酸和乳酸的转化和产氢。结果表明,培养时间为44h时,厌氧活性污泥发酵葡萄糖的累计产气量为356mL,累计产氢量为209mL,氢气含量为58.7%。发酵产物的组成成分乙醇为427.1mg/L、乙酸为716.5mg/L、丙酸为172.5mg/L、丁酸为689.4mg/L、戊酸为123.6mg/L。发酵生物制氢反应器厌氧活性污泥中产氢产乙酸菌群能够对乙醇和乳酸进行产氢产乙酸转化,厌氧污泥转化乙醇形成的乙酸含量约为270mg/L,累计产氢量为15mL;转化乳酸形成的乙酸含量约为190mg/L,累计产氢量为7mL。厌氧污泥不能对乙酸、丙酸、丁酸和戊酸进行产氢产乙酸转化,培养过程中也没有气体生成,分析认为产氢产乙酸菌群对挥发酸的转化不是发酵生物制氢反应器产氢的主要途径。     

氨氮对餐厨垃圾厌氧发酵产氢的影响

研究了以尿素作为氮源时对餐厨垃圾厌氧发酵产氢的影响.研究结果表明,随着尿素添加量的增大,体系中氨氮的浓度逐渐增大,当氨氮浓度在3.58～7.89g/L的范围内,对氢气的产生有促进作用;氨氮浓度超过7.89g/L时,体系的氢气产量开始下降,氨氮浓度为6.24g/L时得到最大氢气产率(126.8mL/g VS);然而,当氨氮浓度超过5.93g/L时,体系反应的延迟时间超过了13.64h,因此综合考虑氢气产量和产氢效率,应该控制反应过程中氨氮的浓度低于6g/L.反应后,液相中的主要产物是乙酸和丁酸,随着尿素投加量的增大,体系中丁酸的浓度逐渐减少,乙酸的浓度增大,但两者的浓度和所占总有机酸的比例都约为80%,没有明显变化;丙酸和戊酸含量较少,且变化不大.     

厌氧活性污泥发酵制氢系统中的同型产乙酸作用及其控制

为提高厌氧活性污泥发酵生物制氢反应系统的产氢效能,以CSTR的运行为基础,通过系统活性污泥的间歇培养试验,探讨了同型产乙酸菌群对发酵制氢系统产氢效能的影响,并以CHCl3和二溴乙烷磺酸钠(BES)为抑制剂,研究了抑制同型产乙酸菌群活性的方法。结果表明:CSTR发酵产氢系统中,存在较强的同型产乙酸作用,是导致发酵气氢含量较低的主要原因;向反应体系中投加0.1%~1.0%(V/V)的CHCl3,可有效抑制同型产乙酸作用;在初始葡萄糖浓度5000mg/L、pH=7.0、污泥接种量1.6g MLVSS/L等条件下,CHCl3加入量为0.5%时,活性污泥的比产氢速率可达8.9mmolH2/gMLVSS,是不加抑制剂反应体系的2倍。10mmol/L剂量的BES,不仅对同型产乙酸菌无抑制作用,且可削弱CHCl3的抑制效果。     

玉米秸秆厌氧发酵生物制氢放大试验研究

在前期试验的基础上,以牛粪堆肥作为菌种来源,以玉米秸秆作为发酵底物,分别在5 L和30 L反应器中进行厌氧发酵制氢试验.试验结果表明:30L反应器处理底物的能力为15 g/L,5 L反应器为10g/L,其相应的底物最高产氢潜力分别为198.25,109.58 ml/g.5 L反应器和30 L反应器的最佳搅拌速率分别为120,100r/min,累积产氢量分别为5.51,58.50L.发酵过程中微生物的生长符合典型的微生物生长规律.5 L反应器和30 L反应器的气相产物中最高含氢量分别为55%和61%.由液相发酵产物确定两反应器中的发酵均为丁酸型发酵.修正后的Gompezrt产氢动力学模型能够很好地描述两反应器的发酵产氢过程,反应器经过放大后,其产氢性能得到了明显的提高.     

玉米秸秆酶解与厌氧发酵产氢实验研究

以粒度小于0.088 mm秸秆粉的酶解液为底物与热预处理活性污泥(其中TS%为6.77%,VS%为47.90%,COD为36.665 g/L)进行厌氧发酵产氢实验,以累积产氢量和产氢速率为考察指标,研究不同热预处理(100℃水浴)时间、初始p H值、酶解液浓度、发酵温度对厌氧发酵产氢的影响,并利用修正的Gompertz方程对产氢过程进行回归分析,优化出最佳玉米秸秆酶解液厌氧发酵产氢的工艺参数。结果表明:活性污泥利用玉米秸秆酶解液进行厌氧发酵产氢时,当活性污泥热预处理时间为15 min、初始p H值为5.0、玉米秸秆粉酶解液浓度为22.34 mg/m L、发酵温度为40℃时,产氢效果最佳,此时最大累积产氢量达到653.98 m L,最大产氢速率为15.89 m L/h。     

基于UASB反应器的厨余厌氧发酵产氢研究

针对目前厨余连续流发酵产氢处理负荷不高、产氢率较低的难题,采用UASB反应器进行厨余发酵产氢研究。在温度为30℃,进水COD浓度为2 000~10 000 mg/L,水力停留时间为2~6 h条件下,产氢速率最大达到17.04 L/(L.d)。反应器内有颗粒污泥的形成,平均生物量达到6.17 g/L,为氢气的产生提供了有利保障。当出水pH为4.2~4.4,碱度为260~340 mg/L的条件下,乙醇和乙酸占挥发酸总量的89.2%,形成稳定的乙醇型发酵类型,反应器最高处理负荷COD达到60 kg/(m3.d)。试验结果表明,UASB反应器具有更高的产氢效能和更加稳定的产氢效果,能够为厨余发酵产氢提供有利的保障。     

微波-盐酸水解啤酒糟对其发酵产氢的影响

以啤酒糟为底物的厌氧发酵产氢技术可以同时实现废物资源再利用和清洁能源生产。为提高啤酒糟的产氢能力,探讨微波-盐酸预处理底物对厌氧发酵产氢的影响,将啤酒糟置于质量体积分数为的1%HCl中,在微波下辐射加热10 min,以未处理和微波-盐酸热处理啤酒糟为底物进行批式厌氧发酵产氢试验研究。结果表明:微波-盐酸预处理能显著提升啤酒糟的糖化与产氢能力;预处理后,啤酒糟的初始还原糖浓度是未处理啤酒糟的30倍,最大氢气浓度由23.18%提高到34.18%,产氢率由25.76 m L/g提高到52.81 m L/g;修正的Gompertz方程可以很好地拟合累积产氢量随时间的变化;啤酒糟发酵过程中的挥发性脂肪酸以乙酸和丁酸为主。     

乙酸对发酵产氢过程的抑制影响

以甲酸为发酵原料进行试验,控制发酵料液的pH在4.8左右,试验共分为10组,每组中分别含有不同浓度的乙酸作为抑制剂。采用批量发酵工艺,进行厌氧发酵产氢,研究乙酸在产氢过程中的抑制作用。由试验可知,当乙酸浓度≥7000mg/l时,抑制作用显著,使产气停止。     

固定化光合细菌利用低分子有机酸的产氢特性

通过固定化光合细菌对低分子有机酸进行了光合产氢的批式试验研究.利用修正的Gompertz方程进行产氢动力学分析,并且对产氢过程中pH变化、有机酸的氢转化率以及有机酸初始浓度对产氢的影响等进行了分析.结果表明固定化能提高产氢率,以海藻酸钠为固定化载体的产氢效果最佳.同时发现有机酸产氢存在最佳初始浓度,其中乳酸产氢的最佳初始浓度为0.049mol/L,对于乙酸、丙酸和丁酸这3种小分子羧酸,其最佳初始浓度的大小随着有机酸碳原子数的增加而减小,即乙酸(0.043mol/L)丙酸(0.029mol/L)丁酸(0.022mol/L).乙酸的最大氢转化率最高,达到65.3%.浓度对氢气含量没有影响,而对于乙酸、丙酸和丁酸,氢气含量随着有机酸碳原子数的增加而增大.     

光合细菌小分子酸醇产氢试验研究

以光合产氢混合菌群为研究对象,研究了光合细菌在乙酸、乙醇、乳酸、丁酸几种小分子脂肪酸条件下菌体的生长和产氢特性,详细考察了乙酸和丁酸对光合产氢细菌生长和产氢的影响.研究发现,乙酸、丁酸既是光合细菌良好的生长碳源,也是高效氢供体,光合细菌在乙酸和丁酸条件下产氢率分别达到2.05和2.81molH2/mol.光合细菌以乙酸和丁酸产氢时,乙酸和丁酸的最佳添加浓度均为40mmol/L;光合细菌在乳酸条件下有较高的生长活性,但乳酸并不是光合细菌高效氢供体,光合细菌在乳酸条件下产氢活性较低;乙醇既不是光合细菌良好生长碳源,也不是高效氢供体,乙醇对光合细菌的生长和产氢均有较强的抑制作用.     

Effect of system optimizing conditions on biohydrogen production from herbal wastewater by slaughterhouse sludge

The study evaluates the biohydrogen production from herbal wastewater as the substrate by the enriched mixed slaughterhouse sludge as the seed source. In the following experiments, batch-fermentations are carried out with the optimum substrate concentrations, fermentation pH and fermentation temperature to observe the effects of H₂ production, hydrogen yield and other fermentation end products at different conditions. The hydrogen production is increased as substrate concentration increased up to 8 g COD/L WW, but drastically decreased at 10 g COD/L WW. When the pH of fermentation is controlled to 6.5, a maximum amount of hydrogen yield could be obtained. The hydrogen production is maximum at 50 °C (930 ± 30 mL/L WW) compared to 30 °C (436 ± 16 mL/L WW). Acid-forming pathway with butyric acid as a major metabolite dominated the metabolic flow during the hydrogen production. The experimental results indicated that effective hydrogen production from the herbal wastewater could be obtained by thermophilic acidogenesis at proper operational conditions.     

Fermentative hydrogen production with xylose by Clostridium and Klebsiella species in anaerobic batch reactors

Hydrogen production was obtained from low concentrations of xylose metabolized by heat treated inoculum obtained from the slaughterhouse wastewater treatment UASB reactor installed in Brazil. The molecular biological analysis Clostridium and Klebsiella species, recognized as H₂ and volatile acid producers, in addition to Burkholderia species and uncultivated bacteria. The assays were carried out in batch reactors: (1) 630.0 mg xylose/L, (2) 1341.0 mg xylose/L, (3) 1848.0 mg xylose/L and (4) 3588.0 mg xylose/L. The following yields were obtained: 3% (0.2 mol H₂/mol xylose), 8% (0.5 mol H₂/mol xylose), 10% (0.6 mol H₂/mol xylose) and 14% (0.8 mol H₂/mol xylose), respectively. The end products obtained were acetic acid, butyric acid, methanol and ethanol in all of the anaerobic reactors. The concentrations of xylose did not inhibit microbial growth and hydrogen production. This suggested that low concentrations of xylose should be added to wastewater to produce hydrogen.     

Sequential fermentation of hydrogen and methane from steam-exploded sugarcane bagasse hydrolysate

The goal of this study was to sequential fermentation of hydrogen and methane from sugarcane bagasse (SCB). Steam explosion conditions for pretreating SCB were optimum at 195 °C and 1.5 min, which yielded 36.35 g/L of total sugar and 2.35 g/L of total inhibitors. Under these conditions (all in g/L): glucose, 11.33; xylose, 24.41; arabinose, 0.61; acetic acid, 2.33; and furfural, 0.02 were obtained. The resulting hydrolysate was used to produce hydrogen by anaerobic mixed cultures. A maximum hydrogen production rate of 396.50 mL H₂/L day was achieved at an initial pH of 6 and an initial total sugar concentration of 10 g/L. The effluent from the hydrogen fermentation process was further used to produce methane. Response surface methodology with central composite design was used to obtain the suitable conditions for maximizing methane production rate (MPR). An MPR of 185.73 mL/L day was achieved at initial pH, Ni and Fe concentrations of 7.59, 3.61 mg/L and 8.44 mg/L, respectively. Total energy of 304.11 kJ/L-substrate was obtained from a sequential fermentation of hydrogen and methane. This approach will not only add value to SCB, in the form of safe and clean energy, but also provide a solution for making use of this abundant waste.     

Enhancement of fermentative hydrogen/ethanol production from cellulose using mixed anaerobic cultures

Batch tests were conducted to evaluate the enhancement of hydrogen/ethanol (EtOH) productivity using cow dung microflora to ferment α-cellulose and saccharification products (glucose and xylose). Hydrogen/ethanol production was evaluated based on hydrogen/ethanol yields (HY/EY) under 55 °C at various initial pH conditions (5.5–9.0). Our test results indicate that cow dung sludge is a good mixed natural-microflora seed source for producing biohydrogen/ethanol from cellulose and xylose. The heat-pretreatment, commonly used to produce hydrogen more efficiently from hexose, applied to mixed anaerobic cultures did not help cow dung culture convert cellulose and xylose into hydrogen/ethanol. Instead of heat-pretreatment, the mixed culture received enrichments cultivated at 55 °C for 4 days. Positive results were observed: hydrogen/ethanol production from fermenting cellulose and xylose was effectively enhanced at increases of 4.8 (ethanol) to 8 (hydrogen) and 2.4 (ethanol) to 15.6 (hydrogen) folds, respectively. In which, the ethanol concentration produced from xylose reached 4–4.4 g/L, an output comparable to that of using heat-treated sewage sludge and better than that (1.25–3 g/L) using pure cultures. Our test results show that for the enriched cultures the initial cultivation pH can affect hydrogen/ethanol production including HY, EY and liquid fermentation product concentration and distribution. These results were also concurred using a denaturing gradient gel electrophoresis analysis saying that both cultivation pH and substrate can affect the enriched cow dung culture microbial communities. The enriched cow dung culture had an optimal initial cultivation pH range of 7.6–8.0 with peak HY/EY values of 2.8 mmol-H₂/g-cellulose, 5.8 mmol-EtOH/g-cellulose, 0.3 mol-H₂/mol-xylose and 1 mol-EtOH/mol-xylose. However, a pH change of 0.5 units from the optimal values reduced hydrogen/ethanol production efficiency by 20%. Strategies based on the experimental results for optimal hydrogen/ethanol production from cellulose and xylose using cow dung microflora are proposed.     

Hydrogen production characteristics from dark fermentation of maltose by an isolated strain F.P 01

A hydrogen producing strain F.P 01 was newly isolated from cow dung sludge in an anaerobic bioreactor. The strain F.P 01 was a mesophilic and facultative anaerobic bacterium, which exhibited gram-negative staining in both the exponential and stationary growth phases, and a regular long rod-shaped bacteria with the size of 0.6–0.9 μm × 1.2–2.5 μm, and also could biodegrade a variety of carbohydrates such as glucose, xylose, maltose, etc. The effects of important process parameters on hydrogen producing of F.P 01 were further investigated from hydrogen fermentation of maltose by strain F.P 01, including substrate concentration, medium pH, etc. And the results showed that hydrogen production potential and hydrogen production rate from maltose of this strain F.P 01 was180 mLH₂/g-maltose and 4.0 mLH₂/h, respectively. The corresponding hydrogen concentration of 58–73% was also be observed. Both butyric acid and acetic acid as main by-product was left in the reactor.     

Biohydrogen production from mixed xylose/arabinose at thermophilic temperature by anaerobic mixed cultures in elephant dung

Biohydrogen production by batch fermentation of mixed xylose/arabinose at thermophilic temperature using anaerobic mixed cultures in elephant dung as the seed inoculums was investigated. Elephant dung was heat-treated in boiling water for 2 h before used as the seed inoculum in order to inhibit methanogenic activity. Biohydrogen was successfully produced from mixed xylose/arabinose. The optimum conditions for hydrogen production were the initial concentration of mixed xylose/arabinose 5 g/L each, initial cultivation pH 5.5 and temperature 55 °C. Under the optimum conditions, a maximum hydrogen yield of 2.49 mol-H₂/mol-sugar consumed was obtained. The optimum conditions were then used to produce hydrogen from sugar derived from acid-hydrolysed sugarcane bagasse (SCB) at a reducing sugar concentration of 10 g/L in which a lower hydrogen yield of 1.48 mol-H₂/mol-sugar consumed was achieved. Main soluble product was acetate suggesting the hydrogen fermentation from mixed xylose/arabinose is the acetate type. The dominant hydrogen producers found in both fermentation broth were Thermoanaerobacterium thermosaccharolyticum and Clostridium sp. Lower hydrogen yield in the SCB hydrolysate fermentation broth may be due to the present of Clostridium ragsdalei and microorganisms in the class Bacilli viz. Lactococus lactis subsp., Lactobacillus delbrueckii, and Sporolactobacillus sp. as well as the inhibitors (acetic acid and furfural) contained in the SCB hydrolysate.     

Influence of pH on fermentative hydrogen production from sweet sorghum extract

The present study focused on the influence of pH on the fermentative hydrogen production from the sugars of sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time of 12 h and a pH range of 3.5–6.5. The maximum hydrogen production rate and yield were obtained at pH 5.3 and were 1752 ± 54 mL H₂/d or 3.50 ± 0.07 L H₂/L reactor/d and 0.93 ± 0.03 mol H₂/mol glucose consumed or 10.51 L H₂/kg sweet sorghum, respectively. The main metabolic product at this pH value was butyric acid. The hydrogen productivity and yield were still at high levels for the pH range of 5.3–4.7, suggesting a pH value of 4.7 as optimum for hydrogen production from an economical point of view, since the energy demand for chemicals is lower at this pH. At this pH range, the dominant fermentation product was butyric acid but when the pH culture sharply decreased to 3.5, hydrogen evolution ceased and the dominant metabolic products were lactic acid and ethanol.     

Effect of operation parameters on anaerobic fermentation using cow dung as a source of microorganisms

Anaerobic fermentation by microorganisms is a promising method of hydrogen production for it can be conducted at mild conditions. In this paper, a series of tests were carried out to investigate the effect of pH, hydraulic retention time (HRT), temperature (T) and substrate concentration on anaerobic dark fermentation. Glucose was utilized as model substrate. The Taguchi orthogonal array was applied in the experimental design and a verification experiment was tested. The results showed the optimal parameters for hydrogen production were pH 5.0, HRT 8.34 h, T 33.5 °C and substrate concentration of 14 g/L, with hydrogen yield of 2.15 mol H₂/mol glucose. Butyric-type fermentation occurred in most tests. According to the analysis of effluent contents, at pH 5.5, 5.0, 4.0, the effluent contained mostly butyric acid (43.1–56.6%), followed by acetic acid (24.6–29.8%); at HRT 4.17, 6.26, 8.34 h, the effluent contained mostly butyric acid (43.0–53.6%). Increasing temperature from 29 to 39.5 °C resulted in the decrease of butyric acid percentage but increase of ethanol percentage. Substrate concentration had little effect on product constitution.